handling nodeJs input from console?

Question

I am still new to nodeJs, and I am trying to create a stream of inputs but my code is not working once I launch the app in the terminal by calling node fileName .

My input format is like this:

- N the number of queries.
- second line represent a string containing two words separated by a space.
- N lines of a string containing two words separated by a space.

for some reason, the terminal doesn't show a thing.

This is my code :

'use strict';
const fs = require('fs');
var n = 0;
var position = '';
var destination = '';
var array = [];


process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', inputStdin => {
    inputString += inputStdin;
});

process.stdin.on('end', _ => {
    inputString = inputString.replace(/\s*$/, '')
        .split('\n')
        .map(str => str.replace(/\s*$/, ''));

    main();
});

function readLine() {
    return inputString[currentLine++];
}
function main() {
    const ws = fs.createWriteStream(process.env.OUTPUT_PATH);


    const s =  parseInt(readLine(), 10);

    const input= readLine().split(' ');

    position = input[0] ;
    destination = input[1];

    console.log('our number is',s, 'and our position and destination:', position, destination);

    ws.end();
}

Your code mostly works. You are reading from stdin, which causes the terminal to lock up until EOF. If you are creating a filter program, this is fine. If not, you'll need to open a different ReadableStream. const ws = fs.createWriteStream(process.env.OUTPUT_PATH); this is also throwing an error. You should just write to stdout when you receive data and use shell io redirection to output to a file. — Rafael
– Rafael, Commented Sep 9, 2018 at 22:39

Rafael · Accepted Answer · 2018-09-09 22:47:34Z

1

You can simplify this whole thing by allowing readline to buffer the input:

'use strict';

const readline = require('readline');

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

rl.on('line', line => {
    rl.write(
        line.replace(/\s*$/, '')
    );
});

answered Sep 9, 2018 at 22:47

Rafael

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3 Comments

oflcad Over a year ago

just want to ask what do you mean by buffering the input ??

Rafael Over a year ago

Great question! In your original code, on data, you were += chunks to a string. This is called buffering, when you take a piece by piece and throw it into larger storage---think of video streaming. Readline takes care of this for you, greatly simplifying the code. The stream's internal buffer may be tiny, taking a little data at a time from the source, but a little data isn't meanful, so you build it into a larger part, that is buffering. In this case, we are doing line-buffered io.

Rafael Over a year ago

To drive this home, imagine a large video, it's unlikely to fit into memory, and the reality is, you wouldn't need to (since the user is only seeing one video frame at a time). If the playback speed is faster than getting data, the video freezes up and has to wait for more data from the stream's source---buffering.

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